Noise-reduction transformers have a filter function against conductive noise transmission. Several types of noise-reduction transformers have been presented. Few papers, however, have reported a noise-reduction transformer for direct power supply to electronics equipments. In this paper, we propose a prototype step-down noise-reduction transformer suitable for digital circuit. The input voltage of the transformer is 100 V and the output voltage is 5 V. Frequency characteristics of noise attenuation are discussed and prevention of pulse noise transmission is demonstrated. The results of the experiments can be summarized as follows: (1) Normal mode noise attenuation is -70 dB, and common mode exceeds -80 dB; (2) Prototype step-down noise-reduction transformer eliminates pulse noise efficiently. Our noise-reduction transformer has a good noise attenuation characteristic and is an efficient noise attenuator.
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